1. Field of the Invention:
The present invention pertains to compositions for inhibiting stress cracking in plastic articles of manufacture, and methods of using those compositions. More particularly, the present invention concerns aqueous-based fatty acid lubricant compositions containing such stress crack inhibitors and methods of using the same. Even more particularly, the present invention concerns aqueous fatty acid-based lubricant concentrates and use solutions prepared therefrom which contain such stress crack inhibitors, and methods of applying the use solutions to poly(alkylene terphthalate) articles to inhibit stress cracking therein.
2. Prior Art:
As is known to those skilled in the art to which the present invention pertains, there has been an ever increasing usage of synthetic resinous containers for fluids and solids. Likewise, as is known to those skilled in the art, such containers are normally filled or washed by passing them through filling and capping stations or through a washing system along manually, mechanically or electronically-operated conveyor systems.
In order to ensure efficient operation of the filling or washing systems it is essential that the conveyor systems, per se, be continuously lubricated. Otherwise, the containers may stack up along the conveyor system and their movement become impeded.
Thus, the conveyors are, ordinarily, continuously lubricated by applying to the conveyor a lubricant, such as by spraying or the like. Typically, conventional lubricants contain alkaline materials, alcohols and other constituents which have a deleterious effect on the plastic articles disposed along the conveyor system.
Indeed, it has long been known that exposure of such articles to these lubricants leads to a phenomenon which as been identified as "stress cracking" which is especially prevalent in poly(alkylene terephthalate) containers and other such plastic articles of manufacture. This is true with respect to both poly(ethylene terephthalate) and poly(butylene terephthalate) containers.
As noted, conventional prior art aqueous-based lubricants containing alcohols and/or alkaline compounds do not inhibit or prevent stress cracking in such containers, but rather, promote stress cracking.
Heretofore, the only proposed prior art method of inhibiting stress cracking in plastic bottles known to the applicants, has been the incorporation of an alkali metal salt of a hydrophilic substituted aromatic hydrocarbon and other hydrotropes into a liquid bleach, such as disclosed in Colborn, European Patent Application No. EP 302705 A2, filed Feb. 8, 1989. This application discloses the use of the hydrotropes as an internal adjustment to the bleach to inhibit stress cracking in high density polyethylene containers. Yet, the art has not directed itself to lubricants and other media for applying a dilute aqueous solution to the exterior of an article to inhibit stress cracking in polyethylene or polybutylene terephthalate bottles or other plastic articles of manufacture. Moreover, the prior art has not recognized the utility of using amines to inhibit stress cracking in plastic articles.
In the above-identified copending U.S. patent Applications, the disclosures of which are hereby incorporated by reference, there are disclosed fatty acid-based conveyor lubricants containing alkyl amines as coupling or saponifying agents for the fatty acid and an alkyl aryl sulfonate as a solubilizing agent for the fatty acid.
The copending applications further teach that the alkyl aryl sulfonates tend to inhibit stress cracking in poly(alkylene terephthalate) articles, such as beverage containers and the like. Furthermore, the copending applications teach that amines can be used in the formation of conveyor lubricants which are highly dilutable and which inhibit stress cracking.
According to the copending applications, it was necessary, to essentially reformulate prior, well-known conveyor lubricants in order to achieve the desired results. For example, conventional prior art conveyor lubricants, as usually found in bottling operations, typically employ an alkali metal hydroxide, such as potassium hydroxide, and/or a glycol, such as hexylene glycol as a low temperature stabilizer. However, both types of compound, i.e., alkali metal hydroxide and glycols are well known promoters of stress cracking in poly(alkylene terephthalate) beverage containers and similar articles.
Thus, it would be highly desirable if the advantages of compositions of the copending applications could be imbued with the conventional prior art components. It is this need to which the present invention is directed.